Trying to define Christian speculative fiction is sometimes like trying to herd chickens or sweep water, but The Lost Genre Guild has made a strong effort. Take a look at their definition here.
Check out their examples in the left column. They've done a nice job enlarging the boundaries for Christian speculative fiction to include topics I hadn't thought of. How about space opera? Or cyberpunk?
Their list of featured books include some recent offerings that are excellent, such as Shade and Never Ceese. Take a look.
And check out these blogs for more offerings about this helpful website:
CSFF Blog Tour
D. G. D. Davidson
Todd Michael Greene
Lost Genre Guild
Rebecca LuElla Miller
John W. Otte